1. Field of the Invention
This invention relates to a production method for a thermoplastic resin compound, in particular, a thermoplastic resin compound comprising a polyester resin mainly based on a polyalkylene terephthalate and a polyphenylene ether resin mainly based on a polyphenylene ether, which can be processed into moldings with enhanced heat resistance and impact resistance.
2. Description of the Prior Art
Thermoplastic polyester resins such as those based on polyalkylene terephthalate, for their good moldability, mechanical properties, thermal stability, and electrical insulation properties, are used in a wide range of applications such as electric and electronic parts and automotive parts. However, conventional art thermoplastic polyester resins are low in rigidity at high temperatures and in impact resistance, in particular, to notch impact, and thus cannot be used in automotive exterior panels for on-line painting.
With the aim of improving the high-temperature rigidity and impact resistance of thermoplastic polyester resins, Japanese Patent Publication Laid-open Nos. 63-500387/1988, 62-121760/1987, 62-121757/1987, 62-129343/1987, and 62-129342 disclose resin compounds comprising the above resin mixed with a polyphenylene ether resin and an impact resistance improver. These resin compounds are improved in terms of high-temperature rigidity and impact resistance, and thus are expected to be applied to applications to which conventional thermoplastic polyester resins could not be applied.
However, in the resin compounds disclosed in the above patents, the polyphenylene ether resin and the polyester resin differ in glass transition temperature by nearly 200.degree. C. Therefore, these resins, when kneaded using an ordinary twin-screw extruder, tend to cause generation of shear heat. In particular, when an extruder having a high shear rate, such as an extruder with a diameter of 40 mm or more, a type which is used in commercial production, is used, these resins tend to decompose due to large amounts of heat generated during extrusion, leading to deterioration in properties of the resins. Use of a single-screw extruder tends to have an insufficient kneading effect, resulting in lumps of unmolten polyphenylene ether resin in the molding.